1. Field of the Invention
The present invention relates to a linear motion guide unit, and more particularly, to a linear motion guide unit that is capable of preventing the variation in the position of a roller cage assembly caused by sliding motions of the roller cage assembly between a first guide rail and a second guide rail, without reducing the number of rollers.
2. Background of the Related Art
Generally, a linear motion guide unit is used for machining tools each having a fixed body and a moving table linearly moved on the fixed body, and it includes a first guide rail fixed to one side of the fixed body or the moving table, a second guide rail fixed to the other side of the fixed body or the moving table, and a roller cage assembly disposed to be rolled between the first guide rail and the second guide rail so as to allow the relative linear motion between the first guide rail and the second guide rail to be gently carried out.
FIG. 1 is a perspective view showing a linear motion guide unit according to a conventional practice, and FIG. 2 is a sectional view showing the linear motion guide unit of FIG. 1. Further, FIG. 3 is a perspective view showing a sliding prevention linear motion guide unit according to another conventional practice, and FIG. 4 is a sectional view showing the sliding prevention linear motion guide unit of FIG. 3.
In the description as will be explained below, a direction perpendicular to the ground in FIG. 2 becomes the direction of the length of the linear motion guide unit.
Generally, a linear motion guide unit 1 is a part installed in machining tools each having a fixed body (not shown) and a moving body (not shown) linearly moved on the fixed body so as to achieve relative linear motions in a gentle manner.
In more detail, the linear motion guide unit 1 includes a first guide rail 10 fixedly disposed on one side of the fixed body, a second guide rail 20 disposed on the moving table so as to perform a relative linear motion with respect to the first guide rail 10, and a roller cage assembly 30 disposed between the first guide rail and the second guide rail so as to perform a rolling motion therebetween.
The roller cage assembly 30 includes a plurality of rollers 35 and a cage plate 45 on which a plurality of roller installation openings 41 is formed to rotatably insert the plurality of rollers 35 thereinto. That is, the plurality of rollers 35 is rotatably inserted into the plurality of roller installation openings 41 formed to be spaced apart from one another by a given distance along the direction of the length of the cage plate 45, such that the plurality of rollers 35 are disposed spaced apart from one another by a given distance.
The first guide rail 10 has a track portion 15 having a pair of rolling faces 11 and 12 formed to have a V-shaped concaved section, and in the same manner as the first guide rail 10, the second guide rail 20 has a track portion 25 having a pair of rolling faces 21 and 22 formed to have a V-shaped concaved section. Further, the first guide rail 10 and the second guide rail 20 have track grooves 13 and 23 more concavedly formed than the pairs of rolling faces 11 and 12, and 21 and 22 in the direction of the length along the center of the track portions 15 and 25. At this time, the track portion 15 of the first guide rail 10 is disposed to be opposite to the track portion 25 of the second guide rail 20.
Moreover, the plurality of rollers 35 in the roller cage assembly 30 is disposed on the cage plate 45 in such a manner as to allow the rotary center lines of the adjacent rollers 35 to be repeatedly crossed to one another. Therefore, each roller 35 performs the rolling motion in the state of being brought into contact with the two facing rolling faces of the four rolling faces 11, 12, 21 and 22 forming the two track portions 15 and 25 facing each other.
In FIGS. 1 and 2, a reference numeral 5 denotes a deviation prevention screw 5 disposed on the end portion of the first guide rail 10 to restrict the rolling motion of the roller cage assembly 30, and 33 denotes a roller-grasping protrusion formed protrudedly on each of the plurality of roller installation openings 41 formed on the cage plate 45 so as to prevent the roller 35 rotatably inserted into each roller installation opening 41 from being deviated therefrom.
The roller cage assembly 30 is desirably movable to an appropriate position between the first guide rail 10 and the second guide rail 20 in correspondence with relative position variations between the first guide rail 10 and the second guide rail 20. In case of the linear motion guide unit 1 according to the conventional practice, however, if the roller cage assembly 30 performs a sliding motion between the track portions 15 and 25, that is, if a sliding motion, not a rolling motion, occurs between the plurality of rollers 35 and the rolling faces 11, 12, and 22 constituting the track portions 15 and 25, unfortunately, the roller cage assembly 30 may have relative position variations between the first guide rail 10 and the second guide rail 20.
If the first guide rail 10 and the second guide rail are used in the state of being disposed vertically with respect to a horizontal surface, especially, the above-mentioned problem may cause the roller cage assembly 30 to be slid and dropped between the first guide rail 10 and the second guide rail 20 by means of its own gravity, with a result that the roller cage assembly 30 is deviated from a given required position, thereby failing to perform its original function.
So as to solve the above-mentioned problems, there has been proposed the sliding prevention linear motion guide unit as shown in FIGS. 3 and 4.
The sliding prevention linear motion guide unit 1′ according to the conventional practice includes a roller cage assembly 30′ further having a rotary shaft 51 disposed parallel to a width direction of the case plate 45 and a pinion 50 mounted rotatably around the rotary shaft 51, a pair of racks 60 disposed inside the track grooves 13 and 23 of the first guide rail 10 and the second guide rail 20 in the direction of the length thereof in such a manner as to be engaged with the pinion 50 to prevent a sliding motion from occurring. In other words, the pinion 50 is positioned, while being engaged with the rack 60 disposed along the track groove 13 of the first guide rail 10 and at the same time with the rack 60 disposed along the track groove 23 of the second guide rail 20, such that the roller cage assembly 30′ is moved in the state of being dependent upon the relative linear motion between the first guide rail 10 and the second guide rail 20. Accordingly, even in the case where a sliding motion occurs on the individual rollers 35, the roller cage assembly 30′ can be located at an appropriate position corresponding to the relative position variation between the first guide rail 10 and the second guide rail 20.
In case of the sliding prevention linear motion guide unit 1′, however, the pinion 50 is rotated around the rotary shaft 51 disposed parallel to the width direction of, the cage plate 45, as shown in FIG. 3, thereby occupying the space of the cage plate 45 on which the rollers 35 should be mounted, and therefore, if other conditions in the sliding prevention linear motion guide unit 1′ are the same as in conventional linear motion guide units, the number of rollers 35 the roller cage assembly 30′ has should be unavoidably reduced. The reduction of the number of rollers 35 in the same conditions undesirably causes the load supported by the roller cage assembly 30′ to be decreased. For example, if a small-sized roller cage assembly 30′ having two or three rollers 35 is made, one of the two or three rollers 35 should be removed to mount the pinion 50, which substantially increases the percentage of the decrease of the supportable load, thereby making it impossible to make the roller cage assembly 30′ itself.
As mentioned above, the reduction of the load supported by the roller cage assembly 30′ causes the linear motion between the first guide rail 10 and the second guide rail 20 to be not performed gently, causes the shortening of the life span, and in some cases, causes the normal rolling motion to be not performed at all. Therefore, this provides serious problems.